Field sequential display systems that have a field sequential display that displays a plurality of images on a time-division basis and a liquid crystal shutter eyeglass have been proposed and developed.
As field sequential display systems, for example three-dimensional display systems that allow the viewer to perceive three-dimensional images, are known.
FIG. 1 is a schematic diagram exemplifying a three-dimensional display system. In FIG. 1, the three-dimensional display system includes liquid crystal display device 100 that is a field sequential display and liquid crystal shutter eyeglass 101. Liquid crystal shutter eyeglass 101 has a liquid crystal shutter 101a for right-eye and a type liquid crystal shutter 101b for left-eye.
Liquid crystal display device 100 alternately displays images for right eye and images for left eye. Right-eye type liquid crystal shutter 101a and left-eye type liquid crystal shutter 101b individually change between a light transmitting state in which light is caused to transmit and a light shading state in which light is caused to be shaded in synchronization with images for right eye and images for left eye that are displayed. Thus, images for right eye enter the right eye of viewer 102, whereas images for left eye enter the left eye of viewer 102. If images for right eye and images for left eye are images that cause a parallax on the right and left eyes, these images can cause the viewer to perceive three-dimensional images.
As field sequential display systems, multi-view display systems that cause a plurality of viewers to perceive different images are known. A multi-view display system is presented in Patent Literature 1. The structure of the multi-view display system is the same as that of the three-dimensional display system shown in FIG. 1.
In the multi-view display system, liquid crystal display device 100 successively displays images for a plurality of viewers. Liquid crystal shutter eyeglass 101, that each of the plurality of viewers wears, changes between the light transmitting state and the light shading state in synchronization with images displayed for the viewers. As a result, the multi-view display system can cause a plurality of viewers to perceive different images.
FIG. 2 is a descriptive diagram exemplifying the operation of a multi-view display system. In FIG. 2, three viewers 102a to 102c respectively wear liquid crystal shutter eyeglass 101.
Liquid crystal display device 100 successively displays image A1, image B1, image C1, and image A2. Liquid crystal shutter eyeglass 101 of viewer 102a changes to the light transmitting state when images A1 and A2 are displayed; liquid crystal shutter eyeglass 101 changes to the light shading state when other images are displayed. Thus, viewer 102a successively perceives images A1 and A2.
Likewise, liquid crystal shutter eyeglass 101 of viewer 102b changes to the light transmitting state when image B1 is displayed; liquid crystal shutter eyeglass 101 changes to the light shading state when other images are displayed. Likewise, liquid crystal shutter eyeglass 101 of viewer 102c changes to the light transmitting state when image C1 is displayed; liquid crystal shutter eyeglass 101 changes to the light shading state when other images are displayed. Thus, viewer 102b perceives image B1, whereas viewer 102c perceives image C1.
As a result, viewers 102a to 102c perceive different images.
As field sequential display systems, a secure display system that causes only viewers who wear a liquid crystal shutter eyeglass to perceive images is known. With a display for a portable information terminal such as a note-type personal computer as a field sequential display, a secure display system can function as a highly secured portable information terminal.
FIG. 3 is a schematic diagram exemplifying a secured display system.
In FIG. 3, field sequential display 104 of portable information terminal 103 alternately displays images and their inverted images, for example, image A, inverted image A′ of image A, image B, inverted image B′ of image B.
In this case, since a viewer who does not wear liquid crystal shutter eyeglass 101 perceives an achromatic image of which an image and its inverted image have been integrated, he or she cannot perceive images A and B.
In contrast, when liquid crystal shutter eyeglass 101 changes to the light transmitting state in synchronization with images A and B displayed and changes to the light shading state in synchronization with inverted images A′ and B′ displayed, viewer 102, who wears liquid crystal shutter eyeglass 101, can perceive images A and B.
Thus, the secure display system can cause only viewers who wear liquid crystal shutter eyeglass 1 to perceive images A and B.
The liquid crystal shutter eyeglass of the foregoing field sequential display system needs to have a high contrast in which the difference between the amount of light transmitted in the light transmitting state and that in the light shading state is large and need to have a high speed response in which the state is quickly changed between the light transmitting state and the light shading state. Unless these characteristics are satisfied, phenomena in which an image to be shaded is perceived by a viewer (crosstalk) and in which an image displayed darkens arise and thereby excellent display images cannot be provided to the viewers.
In addition, since the alignment state of liquid crystal in which a voltage is applied to liquid crystal of the liquid crystal shutter (ON state) differs from that in which no voltage is applied thereto (OFF state), the transmissivity of the liquid crystal shutter changes. Thus, by changing the state of liquid crystal between the ON state and the OFF state, the liquid crystal shutter changes between the light transmitting state and the light shading state.
However, the period of time during which the ON state of the liquid crystal changes to the OFF state in the case in which a voltage applied to the liquid crystal that lies in the ON state is stopped (OFF state response time) is longer than that for which the OFF state of the liquid crystal changes to the ON state in the case that a voltage is applied to the liquid crystal that lies in the OFF state (ON state response time). Thus, the period of time during which the liquid crystal shutter changes from the light transmitting state to the light shading state differs from that during which the liquid crystal shutter is changed from the light shading state to the light transmitting state. If there is such a time difference, a problem arises a crosstalk or the like occurs and thus excellent display images cannot be provided to the viewers.
As a technique for solving can solve the foregoing problem, a liquid crystal display device presented in Patent Literature 2 and a light control device presented as Patent Literature 3 are known.
In the liquid crystal display device presented in Patent Literature 2, two liquid crystal cells in which nematic liquid crystal is horizontally aligned are stacked such that alignment treatment directions of the liquid crystal cells are orthogonal to each other and polarizing layers are formed on both the principal planes of the stacked liquid crystal cells.
If no voltage is applied to both the liquid crystal cells of the liquid crystal display device, it changes to the light shading state; if voltage is applied to one of the liquid crystal cells, the liquid crystal display device changes to the light transmitting state; and if a voltage is applied to both the liquid crystal cells, the liquid crystal display device changes to the light shading state.
Thus, assuming that the light shading state in the case in which no voltage is applied to both the liquid crystal cells is the initial state, by applying a voltage to one of the liquid crystal cells, the liquid crystal display device changes the light shading state to the light transmitting state, then by applying a voltage to the other liquid crystal cell, the liquid crystal display device changes the light transmitting state to the light shading state. By stopping voltage from being applied to both the liquid crystal cells, the liquid crystal display device is restored to the initial state.
Thus, since both the period of time during which the light shading state is changed to the light transmitting state and the period of time during which the light transmitting state is changed to the light shading state become nearly the same as the ON state response time. As a result, the period of time for which the light transmitting state is changed to the light shading state can be the same as the period of time during which the light shading state is changed to the light transmitting state.
On the other hand, in the light control device presented in Patent Literature 3, two TN type liquid crystal cells are stacked such that the alignment treatment directions of the liquid crystal cells are orthogonal to each other in the state in which no voltage is applied to the cells and polarizing layers are formed on both the principal planes of the stacked liquid crystal cells. If the light control device is driven in the same manner as the liquid crystal display device presented in Patent Literature 2, the period of time during which the light transmitting state is changed to the light shading state can be the same as the period of time during which the light shading state is changed to the light transmitting state.
In addition, as a technique that can realize a high contrast, a liquid crystal display device presented as Patent Literature 4 is known.
In the liquid crystal display device presented in Patent Literature 4, two TN type liquid crystal cells are stacked in such a manner that the alignment axes on the view side of the liquid crystal cells lie within 10° and that polarizing layers are formed above, below, and between the stacked TN type liquid crystal cells. Thus, since two TN type liquid crystal cells are stacked, a higher contrast can be accomplished than in the case of the device composed of one TN type liquid crystal cell.
In addition, as a technique that can realize a high speed response, a liquid crystal device presented in Patent Literature 5 is known.
In the liquid crystal device presented in Patent Literature 5, a liquid crystal layer composed of nematic liquid crystal molecules is sandwiched between two opposite substrates. The liquid crystal device has a hybrid arrangement in which the tilt angle successively varies such that nematic liquid crystal modules are vertically aligned in the vicinity of one substrate and they are horizontally aligned in the vicinity of the other substrate. In addition, the liquid crystal device has a twist arrangement in which nematic liquid crystal molecules have reverse twisting directions with respect to the two substrates.
Experimental results show that the foregoing liquid crystal device has a higher response than ordinary twisted nematic (TN) liquid crystal display devices.